insert into t (n) values (400)
/
insert into t (n) values (400)
/

Then, I ran the first query:

HR@XE> select n
  2  from
  3    (select n,
  4       dense_rank() over(
  5     order by cnt desc) as
  6    rnk
  7     from
  8      (select n,
  9         count(*) as
 10     cnt
 11      from t
 12      group by n)
 13   x)
 14  y
 15  where rnk = 1
 16  /

I got:

         N
----------
       400
       300

When I ran the second query:

HR@XE> select max(n) keep(dense_rank first
  2  order by cnt desc) n
  3  from
  4    (select n,
  5       count(*) cnt
  6     from t
  7     group by n)
  8  /

I got:

         N
----------
       400

Which proves that KEEP…FIRST will only keep one value: the greatest number.

Of course, you could change to first query to select the maximum:

select max(n) from ( ...first query ...)

which effectively makes it return the same result as the one with KEEP in this example.

However, testing stats_mode:

HR@XE> select stats_mode(n) from t;

Returned:

STATS_MODE(N)
-------------
          300

stats_mode does not work in 9i or below.

Thanks for this clarification.

If there are 2 values of n in the table with equal maximum frequencies (i.e. two modes), then the first query will return both top ranked values. The second query will return the maximum of the two top-ranked values.

Also, see:

select stats_mode(n) from t;

… which will return strictly one of the modes, although we can’t predict which one.